1. Field of the Invention
This invention relates to a lenticular lens sheet for a transmissive projection screen in a projection-type of television set, which projects light of an image incident on a backside thereof onto a front side thereof.
In addition, in particular, this invention relates to a lenticular lens sheet for a transmissive projection screen, which projects light of an image from a single image displaying source such as a liquid-crystal displaying unit or a digital micro-mirror device (abbreviated name; DMD).
2. Description of the Related Art
Conventionally, for a large television set, three CRT of red, green and blue are used, and their images are enlarged and projected on a screen through a projecting lens system. In addition, recently, a liquid-crystal projection type of television set has been developed, wherein three liquid-crystal displaying panels of red, green and blue are used and wherein their images are composed and displayed by a dichroic mirror. Furthermore, there is a projection type of television set wherein a liquid-crystal panel or a DMD panel is used and wherein a color display is achieved in a field-sequential manner.
A conventional screen for a CRT has: lenticular lenses on both surfaces thereof, and a black stripe (light blocking stripe) on an observed surface in order to block reflection of any external light. If an LCD panel or a DMD panel is used, as an image source is single, the lens on the observed surface is unnecessary. Thus, a lenticular lens sheet having lenticular lenses on only one surface of a light-source side has been used.
When such a lenticular lens sheet (or a screen having such a lenticular lens sheet) is used, an image observed by an observer should be bright. Especially, when the image source is an LCD panel or a DMD panel, there is a limit to enhancement of illumination of a or more lamps themselves because of costs or lives thereof. Thus, it is requested to enhance the gain of a screen.
In addition, a lenticular lens with a black stripe, which has been used conventionally, is designed in such a manner that a concentrated focal point is in a predetermined area in the vicinity of the black stripe. Thus, with respect to a diffusion characteristic thereof, a xc2xd diffusion angle (an angle range that can obtain xc2xd luminance with respect to luminance at a front area of the screen) is wide, but a peak gain is low. In addition, when an angle from the front area is over xc2x150xc2x0, the gain rapidly declines so that a cutoff happens. Especially, in a lenticular lens sheet with a black stripe of a fine pitch, in order to prevent the cutoff, it is necessary to make positional accuracy in forming the black stripe very severe.
In this invention, an object is to provide a lenticular lens sheet whose peak gain can be enhanced and which can avoid any cutoff. In addition, for a lenticular lens sheet with a black stripe of a fine pitch, it is also an object to facilitate a control, in particular a positional control, in forming the black stripe.
According to the inventors, instead of concentration of focal points by respective points on a lens surface into one point, when focal lengths by the respective points continuously vary from the center of the lens surface toward edges of the lens surface, in particular when the focal lengths shorten toward the edges of the lens surface, if a black stripe is formed in such a manner an area including a focal point by the edges of the lens surface is left as an opening, it can be prevented that light (beams) through the respective points on the lens surface is blocked by the black stripe. In addition, in the case, reflection of external light can be sufficiently reduced by means of the black stripe.
This invention is a lenticular lens sheet comprising: an incidence plane that has a plurality of lens surfaces; and an outgoing plane; wherein a focal length at a center portion of each of the plurality of lens surfaces is longer, and a focal length at an edge portion of each of the plurality of lens surfaces is shorter.
According to the feature, since the focal length at the center portion of each of the plurality of lens surfaces is longer, that is, since refraction at the center portion of each of the plurality of lens surfaces is restrained, luminance at a front area can be enhanced, that is, the peak gain can be enhanced. In addition, if a light blocking portion is formed on the basis of a refracted beam at the edge portion of each of the plurality of lens surfaces, a lenticular lens sheet with a light blocking portion that generates no cutoff can be provided.
Preferably, the outgoing plane is flat. In the case, contrast can be enhanced. In addition, if a hard coating process or a reflection-prevention coating process is conducted to the outgoing plane by an application or the like, the effect may be outstanding, so that the roughness of an image may be reduced and the feel of the image may be also improved. In addition, it is easy to clean the surface of the outgoing plane.
Preferably, in each of the plurality of lens surfaces (in each lens unit), focal lengths at respective points from the center portion to the edge potion shorten in order from the center portion toward the edge potion. More preferably, in each of the plurality of lens surfaces, focal lengths at respective points from the center portion to the edge potion continuously shorten from the center portion toward the edge potion. In the case, each of the plurality of lens surfaces may have a sectional contour consisting of a convex curve.
In addition, preferably, in a sectional contour of each of the plurality of lens surfaces, when a curvature radius at the center portion of each of the plurality of lens surfaces is represented by R, an angle formed by a tangential line at the edge portion of each of the plurality of lens surfaces and a tangential line at the center portion of each of the plurality of lens surfaces is represented by xcex8, a pitch of an arrangement of the plurality of lens surfaces is represented by P, and a thickness and a refractive index of a lens part defining the plurality of lens surfaces are represented by H and n, a following expression
tan { sinxe2x88x921(sin xcex8/n)xe2x88x92xcex8+(xcfx80/2)} less than 2xc3x97{nxc3x97R/(nxe2x88x921)xe2x88x92H}/P
is satisfied.
If the above expression is utilized, a lenticular lens sheet having some advantage can be efficiently designed and manufactured.
Preferably, a pitch of an arrangement of the plurality of lens surfaces is 0.001 mm to 0.3 mm. In the case, if the lenticular lens sheet is used together with an image source of a fine pitch, it can be prevented that a moire pattern appears.
Preferably, a lens part defining the plurality of lens surfaces is layered onto a transparent substrate.
For example, the lens part can be easily formed by hardening a liquid transparent resin or the like.
Preferably, the lens part defining the plurality of lens surfaces consists of an ionization radiation hardening resin. In the case, the shape of the lens part can be formed more precisely. In addition, the lens part can be easily formed even on a resin film.
In addition, preferably, a light blocking portion is formed in a thickness direction of the lenticular lens sheet and in a planar direction of the lenticular lens sheet in such a manner that at least a beam through the edge portion of each of the plurality of lens surfaces is not blocked by the light blocking portion.
In the case, it is secured that a beam incident on and refracted by the edge portion of the lens surface outgoes through the lenticular lens sheet. Thus, with respect to all diffusion angles, a beam can pass through the lenticular lens sheet. Even if a position of the light blocking portion is slightly incorrect or shifted, a beam can still pass at a small diffusion angle. That is, the influence is small on the beam. In a conventional lenticular lens sheet wherein the focal points are concentrated into one point, if a position of the light blocking portion is slightly incorrect or shifted, this has great influence on beam passage (outgoing) with respect to all diffusion angles.
Preferably, the light blocking portion is formed between a level of a focal point corresponding to the center portion of each of the plurality of lens surfaces and a level of a focal point corresponding to the edge portion of each of the plurality of lens surfaces, with respect to the thickness direction of the lenticular lens sheet. In the case, a positioning step for forming the light blocking portion can be easily conducted, and positional accuracy for forming the light blocking portion can be easily secured.
Preferably, when parallel beams are incident on each of the plurality of lens surfaces and luminance at a front area of the outgoing plane is represented by B, an area having luminance not less than B/2 includes xc2x115xc2x0 to xc2x140xc2x0 from the front area, and an area having luminance not less than B/10 further includes xc2x115xc2x0 from the area having luminance not less than B/2.
In the case, a lenticular lens sheet with a light blocking portion having a high peak gain and a wide view angle can be provided.
Preferably, a width of the light blocking portion is 40% to 90% of a pitch of an arrangement of the plurality of lens surfaces. In the case, since the existence rate of the light blocking portion is high, reflection of external light on an observed side can be restrained more surely.
Preferably, the light blocking portion consists of a silver-salt photo emulsion layer that has been developed. In the case, if the silver-salt photo emulsion layer has been exposed by light from a lens-surface side and then developed, the light blocking portion having a high reflection-preventing effect can be formed at high positional accuracy to geometry of the lens.
The above lenticular lens sheet can be used as a backside-projecting type of screen.
In the above screen, the lenticular lens sheet may have a light-diffusion effect. For example, a backside-projecting type of screen with a light-diffusion effect in a direction perpendicular to the light-diffusion direction by means of the original lens part may be provided.
In addition, in the above screen, a light-diffusion element is further provided at least an outgoing part of the screen. The outgoing part means a portion of the outgoing plane except the light blocking portion. The light-diffusion element may be a sheet in which a light-diffusion agent has been dispersed.